Resistance welding apparatus



y 1933- L. R. PETERS 2,123,053 I RESISTANCE WELDING APPARATUS Filed Sept. 25, l956 Inventor": Leo R. Peter-s,

by Jim/ His Attorney.

Patented July 5, 1938 RESISTANCE WELDING APPARATUS "Leo E. Peters, Cleveland, Ohio, assignor to General Electric Company, a corporation of New York Application September 25, 1936, Serial No. 102,552

9 Claims. (or 175-320) My invention relates to an electric timer and to control systems embodying said timer.

It is an object of my invention to provide an electric timer that is inexpensive, easily adjusted.

simple to install with existing equipment and accurate for the usual timing operations required in industry.

It is a further object of my invention to provide a timer that functions in response to the var- 0 iation in the voltage distribution in a circuit the resistance value of a portion of which rapidly changes due to current heating.

Other objects ofvmy invention will become apparent from thefollowing description taken in connection with the accompanying drawing, Fig.

l of which diagrammatically represents one embodiment of my invention as applied to the control of a resistance spot welder, and Fig. 2 of which is a diagrammatic representation of a modification of the-timing circuit forming a part of the system of Fig. 1.

In the system shown in Fig. l the electrodes ill of a resistance spot welding machine are connected to the secondary of a transformer H, the

primary of which is connected to a source of supply I! through a rheostat 'II, the contacts I of a relay l5 and a switch". The operating. winding ll of relay Ii is connected to a timing; circuit in which a thermally variable resistance element It is connected in series with a rheostat It, or similar element, the resistance of which does not vary materially with changes in temperature due to current heating. This timing circuit is connected to the source of supply i2 through as switch I which also connects the transformer circuit to the same source of supply.

The thermally variable resistance element ll may be a standard Mazda lamp the resistance of which rapidly increases with the increase in temm perature of its filament due to current heating. Because of the variation in resistance of the lamp II the voltage distribution in the timing circuit varies, the voltage across the operating winding ll of relay I! at any instant being the line voltage minus the IR. drop across the rheostat It. When the switch It is closed the source of supply is connected to the timing circuit and at the same time through contacts 14 of relay ii to the welding transformer ii. At the first instant the cold I resistance of lamp I8 is low and consequently determined time after its energization result ing from the closure of switch I l.

Satisfactory timing operations have been obtained when the control lamp was of, suchanature that about one-half'cf the welding time was required to bring thevoltage applied to the operating winding of thefrelay'to a value which initiated the movement of its armature and then allowed a still further rise in volage which was sufilcient to actuate the armature and separate the relay contacts. During the first interval the essential variables of the relay are balanced out so that no appreciable changes in the timing can be caused thereby. A

The switch I8 may be connected with the mechanism employed for moving th= electrodes into and out of engagement with the work to be welded so that it is not closed until after the electrodes have been brought into engagement with the work. Such a connection is well known in the art and consequently has not been illustrated in the drawing. After the electrodes have been brought into engagement with the work and the switch It closed, the system above described op- .erates as follows:

The closure of switch It simultaneously completes the transformer circuit and the timing circuit. The transformer circuit is completed as follows: From one terminal of the source of supply i2 through switch it, conductors 2! and 13, contacts H of relay l5, conductor 24, rheostat l3,

conductor 25, the primary of welding transformer II and conductor 26 to the other terminal of the source of supply II. The timing circuit is completed as follows: From one terminal of the source of supply I! through switch it, conductor 22, lamp ll, rheostat l9 and conductor 21 to the other terminal of the source of supply l2. As has been pointed out above, the variation in voltage distribution in this timing circuit with the variation in current fiow therethrough resulting from the variation of the resistance of lamp It eventually applies a voltage to the operating winding ll of relay I5 which causes this relay to operate, opening its contacts I4 and terminating the welding operation which was initiated by the closure of the switch [6.

When the switch I6 is open the timing circuit is deenergized, deenergizing the operating winding I! of relay l5 and its armature is returned to the position illustrated in the drawing through the agency of a biasing spring 28, thus permitting the contacts I of the relay I6 to again close due to the bias imparted thereto by spring 2|. The filament of the lamp ll rapidly cools when the timing circuit in which it is located is deenergized and, consequently, the control of which it forms a part may be operated with great frequency without disturbing the calibration determined by the adjustment oi! rheostat 19.

It is, of course, apparent that instead of using a standard Mazda lamp as part of the timing circuit any thermally variable resistance may be used. This thermally variable resistance may be made of molybdenum, tantalum, etc. having a positive temperature coeflicient of resistance similar to that of the tungsten filament of the standard Mazda lamp, or it may have a negative temperature coefilcient of resistance such as possessed by the filament of a carbon lamp. In either case suitable circuits must be provided in order to cause the thermally variable resistance to function properly.

In Fig. 2 I have diagrammatically represented a timing circuit employing a thermally variable resistance having a negative temperature coefilcient such as the carbon filament lamp referred to. In Fig. 2 the timing circuit is completed through switch 29, carbon filament lamp and rheostat ii. The operating coil ll of the relay i5 is connected across the rheostat and is responsive to the rise in voltage across the rheostat which occurs as the resistance across the lamp 30 decreases as the lamp heats up.

It is, of course, apparent that any circuit in which the voltage distributionvaries with the variation in the resistance value of a portion thereof due to current heating may be employed for operating an electro-responsive device which is connected to be responsive to a voltage variation in said circuit. Thus the particular circuits above illustrated and describedare merely illustrative of electric timing circuits embodying my invention.

Thestandard Mazda lamp IB above referred to may be of the vacuum type or of a type having a gas filling. When a gas filled lamp is employed the system can be operated at about ten times the frequency that is possible when employing a vacuum lamp and still maintain the desired accuracy of timing. This is due to the fact that the filament of a gas filled lamp cools much more rapidly and is enabled to maintain its cold to hot resistance ratio in shorter periods of time than is possible when using a vacuum lamp.

The system described in Fig. 1 has been repeatedly operated at approximately one second intervals when adjusted for a three cycle timing operation and it has been found that the varia-' tion in timing has never been much more than of a cycle when using a. cycle source of supply. With a 10 cycle timing operation, the

greatest variation was about of a cycle. Va1iations in the voltage of the source of supply will aflect the timing obtained and it may be that the variations above noted were the direct result of variations in line voltage and not due to the frequency of operation. By proper selection of the thermally variable resistanceelement and the relay, it is possible to make the variation in time inversely proportional to the square, cube or even directly proportional to the line voltage within a predetermined operating range.

The electric timer above described is easily adjusted by adjusting the rheostat is which may be provided with a time setting indicator having a scale 3| and a pointer 32 giving the time settings obtained at definite line voltages with lamps of various wattage for various adjustments of the rheostat. Thus a scale may be provided for lamps of 40, 60 and '75 watt capacity. The timing becomes more critical with the higher wattage lamps when using the same adjusting rheostat.

Since the timer embodies only a rheostat, a lamp socket, a lamp, a relay and the necessary connections above described, it is apparent that it is not only simple but quite inexpensive. Furthermore, from what has been noted above it is apparent that extremely short periods of time are obtainable by making simple adjustments. The timer is easily installed with existing equipment and when used for welding machines as described above, may be enclosed with the primary rheostat l3 of the welding transformer ll, thus forming a compact unit embodying all the controls for the welder.

My electric timer is particularly suited for timing resistance welding operations in that the timing depends on the line voltage, increasing when the voltage drops and decreasing when the voltage rises, to give a substantially constant watt input to the weld. It is, however. apparent that this electric timer may be used for controlling the operation of any translating device and that it will function on a direct current or alternating current source of supply. It may be used for flashing lamps to obtain a very intense light for photographic or signaling purposes as disclosed in application Serial No. 102,569, George W. Inman, for Method and apparatus for flashing electric discharge devices, filed concurrently herewith and assigned to the same assignee.

Various modifications and applications of my invention will occur to those skilled in the art in view of the particular embodiments above illustrated and described. It is to be understood therefore that I intend to cover all such modifications as fallwithin the true spirit and scope of my invention, as pointed out in the claim: annexed hereto.

What I claim is new and desire to secure by Letters Patent of the United States is:

1. An electric timer comprising a circuit in which a thermally variable resistance element is connected in series with an adjustable resistance element the resistance of which does not vary materially with changes in temperature due to current heating, a voltage responsive device connected across one of said elements, means actuated by said voltage responsive device, a time setting indicator, means for adjusting said adjustable resistance element in accordance with the setting of said indicator, and means for connecting said series connected resistance elements to a source of voltage.

2. An electric timer comprising a circuit in which a lamp having a filament with a positive temperature coefilcient of resistance is connected in series with an adjustable resistor the resistance of which does not vary materially with changes in temperature due to current heating, a relay having an operating winding connected in said circuit in parallel with said lamp, means actuated by said rolay, a time setting indicator, means for adjusting said adjustable resistor in accordance with the setting of said indicator, and means for connecting said series connected lamp and resistor to a source of voltage.

3. An electric timer comprising a circuit in aiaaoos which a gas filled lamp having a filament with a positive temperature coeflicient or resistance is connected in series with an adjustable resistor the resistance or which does not vary materially with changes in temperature due to current heating, a relay having an operating winding connected in said circuit in parallel with said lamp, means actuated by said relay, 2. time setting indicator, means for adjusting said adjustable resistor in accordance with the setting of said indicator, and means for connecting said series connected lamp and resistor to a source 01' voltage.

4. An electric timer comprising a circuit in which a tungsten filament lamp is connected in series with an adjustable resistor the resistance of which does not vary materially with changes in temperature due to current heating, a relay having an operating winding connected in said circuit in parallel with said lamp, means actuated by said relay, a time setting indicator, means for adjusting said adjustable resistor in accordance with the setting of said indicator, and means for connecting said series connected lamp and resistor to a source of voltage.

5. An electric timer control comprising a translating device, a relay having an operating winding and contacts which are normally biased into engagement with one another and which are opened upon a predetermined energization of said operating winding, a circuit in which said relay contacts and said translating device are connected, a circuit in which a thermally variable resistance element is connected in series with an adjustable resistance element the resistance of which is substantially unafiected by temperature variations due to current heating and in which said relay operating winding is connected in parallel with one of said elements, a source 0! supply, and means for simultaneously connecting said translating circuit and said relay operating winding circuit to said source of supply.

6. An electric timer comprising a voltage responsive relay having an operating winding and a control element actuated thereby, means including a rheostat for connecting said operating winding to a source of supply, a time setting indicator, means for adjusting said rheostat in accordance with the setting of said indicator, and a thermally variable resistor connected in parallel circuit with said operating winding of said relay, said thermally variable resistor having a low resistance when cold and heating up very rapidly with the passage of current therethrough from said source of supply so that about half the timing period determined by said electric timer is consumed in building up a voltage across said thermally variable resistor suflicient to initiate the operation of said relay and balance out the essential variables thereof, the further rise in voltage across said thermally variable resistor being sumcient to actuate the control element of said relay.

'7. An electric timer control comprising a translating device, a relay having an operating winding, an armature and contacts which are normally biased into engagement with one another and which are opened by the impact of said armature the movement of which is initiated upon a predetermined energization of said operating winding, a circuit in which said relay contacts and said translating device are connected, a circuit in which a tungsten filament lamp is connected in series with an adjustable resistance element the resistance of which does not vary materially with changes in temperature due to current heating and in which said relay operating winding is connected in parallel with said tungsten filament lamp, a source of supply, means for simultaneously connecting said translating circuit and said relay operating winding circuit to said source of supply, a time setting indicator, and means for adjusting said adjustable resistance element in accordance with the setting of said indicator.

8. An electric timer comprising a voltage responsive relay having an operating winding and a control element actuated thereby, a thermally variable resistance element whose resistance changes rapidly with changes in temperature due to current heating connected in series circuit with an adjustable resistance element whose re-' sistance does not vary materially with changes in temperature due to current heating, and means for connecting said series circuit including said resistance elements to a source of voltage, the operating winding 01 said relay being connected across one of said resistance elements and the rate of change of voltage across said thermally variable resistance element upon being connected with said source being such that about half the timing period determined by said electric timer is consumed in building up a voltage across the operating winding of said relay which is sufficient to initiate its operation.

9. An electric timer control comprising a translating device, a relay having an operating winding and contacts controlled thereby, a circuit in which said relay contacts and said translating device are connected, a circuit in which a thermally variable resistance element is connected in series with an adjustable resistance element the resistance of which is substantially unailected by temperature variations due to current heating and in which said relay operating winding is connected in parallel with one of said elements, a source of supply, and means for simultaneously connecting said translating circuit and said relay operating winding circuit to said source of sup y.

LEO R. PETERS. 

